Current responsive actuator

ABSTRACT

A circuit breaker with a trip latch operable by a thermally sensitive longitudinally expandable plunger enclosed in a conductor casing connected in series with the circuit breaker switch. In one embodiment the conductor casing has a suitable resistance for heating the plunger for tripping the circuit breaker at excessive circuit breaker current levels and in another embodiment the plunger comprises a plurality of longitudinally spaced eddy current heating discs for heating intermediate longitudinally expandable plugs.

0 United States Patent 11 1 1111 3,849,752 Bayer Nov. 19, 1974 [5 CURRENT RESPONSIVE ACTUATOR 2,559,372 7/1951 Rike 337/394 3.117103 1/1964 Hurtle 337/114 [75] lnvemor- Em Bayer wolcotti Conn- 3.453008 8/1969 Teichert et a1 337/394 ox [73] Assignee: General Electric Company, New

York, NY. Primary Examiner-A. T. Grimley [22] Filed: Aug. 2, 1973 21 Appl. No.1 384,985 1571 ABSTRACT A circuit breaker with a trip latch operable by a ther- 52 US. Cl 337/77, 337/106, 337/123, mally sensitive longitudinally expandable Plunger 337/394 closed in a conductor casing connected in series with 51 Int. Cl. H0lh 62/02 the Circuit breaker switchone embodiment the [58] Field f Search 337 /77, 106 114, 123, conductor casing has a suitable resistance for heating 337/128 394 236/5 [9 33 43 59 the plunger for tripping the circuit breaker at exces- 23778 335/142 sive circuit breaker current levels and in another embodiment the plunger comprises a plurality of longitu- [56] References Cited dinally spaced eddy current heating discs for heating UNITED STATES PATENTS intermediate longitudinally expandable plugs.

1,610,552 12/1926 James 337/123 14 Claims, 4 Drawing Figures Pmmm uv I 91914 3'. 949.752

. sum 2 BF 2 CURRENT RESPONSIVE ACTUATOR BRIEF SUMMARY OF THE INVENTION The present invention relates to a new and improved current responsive actuator having notable utility in circuit breakers for tripping the circuit breaker when the circuit breaker current exceeds a designed limit.

It is a principal aim of the present invention to provide a circuit breaker current responsive actuator having a new, improved and more reliable mode of operation for tripping the circuit breaker.

It is another aim of the present invention to provide a new and improved circuit breaker current responsive actuator which may be manufactured in a single standard design to be used in circuit breakers having different designed current limits.

It is another aim of the present invention to provide a new and improved current responsive actuator which provides continuing reliable operation in installations experiencing short circuit or other excessive current levels.

It is a further aim of the present invention to provide a new and improved circuit breaker current responsive actuator which is adjustable to accurately trip the circuit breaker at the desired current level.

It is another aim of the present invention to provide a new and improved circuit breaker current responsive actuator which produces a relatively high trip force and which thereby permits greater design flexibility in the associated circuit breaker trip mechanism.

It is another aim of the present invention to provide a new and improved current responsive actuator having a compact and reliable design with a minimum number of parts and having a substantially unlimited service free useful life.

It is a further aim of the present invention to provide a new and improved low cost current responsive actuator which can be manufactured by automatic and mass production methods.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

A better understanding of the invention will be obtained from the following detailed description and the accompanying drawings of illustrative applications of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the FIGS.:

FIG. 1 is a side view of an electric circuit breaker, with the cover removed, incorporating an embodiment of a current responsive actuator of the present invention;

FIG. 2 is an enlarged side view, partly broken away and partly in section, of the current responsive actuator;

FIG. 3 is an enlarged rear end view of the current responsive actuator; and

FIG. 4 is an enlarged longitudinal section view, partly broken away and partly in section, of a modified embodiment of a current responsive actuator incorporating the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings in detail wherein like numerals represent like parts throughout, an electric circuit breaker l0 incorporating an embodiment 12 of a current responsive actuator of the present invention is, excepting for the actuator 12, similar to the circuit breaker shown and described in US. Pat. No. 3,488,610 of David B. Powell. dated Jan. 6. 1970 and entitled Circuit Breaker With Improved Thermal- Magnetic Tripping Mechanism," and therefore, apart from the actuator 12, will not be described in detail. Briefly, however, the circuit breaker 10 has line and load terminals 16 and 18, and a switch mechanism 20 for making and breaking an electrical connection between the terminals l6, 18. The switch mechanism 20 comprises a switch 22 having a fixed contact 30 electrically connected to the terminal 16 and a pivotal contact arm 31 with a movable contact 32. An operating handle 34 provides for selectively pivoting the contact 32 into and out of engagement with the fixed contact 30, and with the switch 22 closed as shown in FIG. 1, a pivotal latch member 36 biased to its latching position by a spring 37, functions through an upstanding latching tab 38 to latch a cradle 40 in the position shown and thereby hold the circuit breaker switch 22 closed. Slight pivotal movement of the latch member 36 in the counterclockwise direction as viewed in FIG. I effects withdrawal of the latching tab 38 to permit a power spring 42 to withdraw the movable contact 32 from the fixed contact 30 and break the internal electrical circuit between the line terminals 16, 18.

The current responsive actuator 12 comprises a tubular casing 50, which may be a split casing for economy of fabrication, forming an elongated cylindrical chamber 52 for receiving a longitudinally expandable thermally sensitive expansion plunger 53. In the embodiment shown in FIG. 2, the elongated plunger 53 comprises a rear cylindrical expansion plug 54 and a forward generally cylindrical actuating member 55 having a forward rounded end engageable with a depending lever arm 56 of the latch member 36. The split tubular casing 50 is shown formed with opposed axially extending flanges 57, 58 along its circumferential ends and with a plurality of integrally formed longitudinally spaced electrical connectors 59-64 extending outwardly from the circumferential end flanges 57, 58. The forward five electrical connectors 60-64 extend outwardly from one circumferential end flange 57 and the rear electrical connector 59 extends outwardly from the other circumferential end flange 58. A terminal strap is designed to engage a selected one of the forward connectors 60-64 to electrically connect the selected connector 60-64 to the terminal 18 and may, if desired, be suitably secured to the selected connector 60-64. A flexible electrical conductor 66 is connected to the rear electrical connector 59 to provide an electrical connection to the pivotal contact arm 31 and to thereby connect the actuator casing 50 in series with the switch 22 between the terminals l6, 18, the effective conductor length of the actuator casing 50 used in the internal circuit being dependent upon the forward connector 60-64 used.

The expansion plunger 53 is longitudinally positioned within the casing 50 with an adjustment screw 70 threaded through a rear non-rotatable end cap 72 of the tubular casing 50 and supporting a rear thrust washer 74 for the expansion plunger 53.

The casing 50 is made of a suitable sheet metal resistance material having a thickness, for example of between 0.025 to 0.030 inches and such that when the circuit breaker current exceeds a predesigned level the resistance impedance of the tubular casing 50 between the operative connectors is sufficient to quickly heat and thereby longitudinally expand the thermally sensitive expansion plug 54 to trip the circuit breaker. The adjustment screw 70 is properly preadjusted so that the latch member 36 is pivoted to trip the current breaker at the desired current trip level.

Since the rate of heat generation by the casing 50 (and therefore the rate of longitudinal expansion of the thermally sensitive expansion plug 54) is a function of not only the current level, but also the effective conductor length of the casing 50 used in the internal circuit breaker, the current level at which the circuit breaker is tripped can be selected in steps within a predesigned range by selecting the electrical connector 60-64 to which the terminal strap 65 is connected. Thus, a single current responsive actuator design can be used as a latch actuator in circuit breakers with different current ratings. Also, a suitable resistance shunt (not shown) may be connected across the operative electrical connectors 59 and 60-64 and such that only a predesigned portion of the circuit breaker current would be conducted through the casing 50 and whereby a single actuator design could be used with circuit breakers with different current ratings by using resistance shunts with resistances appropriately related to the resistance of the casing 50.

As the electrical connectors 59 and 60-64 are connected to different circumferential edges of the casing 50, the casing current is conducted along substantially the entire casing between the operative electrical connectors and such that substantially the entire casing between the operative connectors serves as a conductor for heating the contained expansion plug.

The cylindrical expansion plug 54 may be formed of particulate material, for example a very fine copper power, or be made solid. The material used should have a high linear coefficient of expansion to provide good responsiveness. Low density polyethelene has the desired high coefficient of expansion, and a low density polyethelene plug 54 l /zto 2 inches long and having a diameter of 3/16 inch has been found to work well. Also, it has been found that such a polyethelene plug formed with embedded copper particles is more responsive because of the added thermal conductivity provided by the copper particles.

A generally U-shaped soft iron magnet member 80 is suitably mounted to partially surround the actuator 12 and so that it is magnetizable by the current conducted along the casing 50, for which reason the casing 50 is constructed of a suitable non-magnetic material such as non-magnetic stainless steel. The latch member 36 functions as an armature for the magnet 80 and is therefore made of a suitable ferromagnetic material, and an air gap is established between the latch member 36 and the poles 82 of the magnet 80 such that a sudden high overload current of a predetermined magnitude will generate sufficient magnetic force to attract the latch member 36 and trip the circuit breaker. The magnetictrip action is therefore practically instantaneously responsive to sudden high current overloads to trip the circuit breaker before the thermally sensitive plunger 53 would respond to trip the circuit bfeaker.

A modified current responsive actuator incorporating the present invention and useful in AC circuit breaker applications is shown in FIG. 4. In that modified embodiment, the plunger 53 comprises, in addition to the forward actuating member 53, a plurality of thermally sensitive heat expandable cylindrical plug sec-- tions 84 (formed like the heated expandable plug 53) and a plurality of intermediate eddy current heating discs 86. The eddy current heating discs 86 are made of a suitable material so as to produce internal eddy current heating within the plunger 53 for heating the adjacent plug sections 84. The eddy current heating disc 86 would be constructed in accordance with the AC frequency and the intended current trip level to produce the desired reactance impedance and the resulting eddy current heating. The number of active eddy current heating discs 86 can be selected with the forward electrical connectors 60-64 and such that as with the embodiment of FIG. 3 a single current responsive actuator design can be used in circuit breakers with different current ratings. Also. where the eddy current heating disc 86 are employed. the casing 50 may or may not be made of a suitable resistance material to provide an additional resistance impedance heating source for heating the plunger 53.

In both embodiments. the components of the plunger 53 are mounted within the casing 50 so that when the plunger 53 cools and longitudinally contracts. the plunger 53 is retracted by the latch spring 37 through the coacting lever arm 56 of the latch member 36. Also, the internal surface of the casing 50 may be suitably polished and/or a light silicon oil lubricant may be applied to the mating surfaces of the casing 50 and plunger 53 to facilitate longitudinal expansion and contraction of the plunger 53 within the casing 50.

As will be apparent to persons skilled in the art. various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.

I claim:

1. in a circuit breaker having a pair of terminals, an internal electrical circuit breaker between the circuit breaker terminals comprising an electrical switch and a current responsive actuator, a switch operating device operable for opening and closing the switch and having a switching member actuated by the current responsive actuator when the actuator current exceeds a predetermined level to open the circuit breaker switch. the improvement wherein the current responsive actuator comprises a thrust support and an elongated thermally sensitive expansion plunger extending longitudinally from the thrust support and longitudinally expandable from the thrust support upon being heated to actuate the switching member to open the switch, the current responsive actuator having an electrical impedance in the internal electrical circuit effective to heat and thereby longitudinally expand the expansion plunger to actuate the switching member to open the switch when the actuator current exceeds said predetermined level.

2. A circuit breaker according to claim 1 wherein the switch operating device comprises spring means for opening the switch and wherein the switching member is operative to latch the switch closed and is actuated by the longitudinal expansion of the expansion plunger to unlatch the switch to be opened with the spring means when the actuator current exceeds said predetermined level.

3. A circuit breaker according to claim 1 wherein the current responsive actuator comprises an elongated electrical conductor casing for the elongated expansion plunger electrically connected in the internal electrical circuit.

4. A circuit breaker according to claim 3 wherein the current responsive actuator comprises a generally U shaped magnetizable magnet member partly surrounding the elongated electrical conductor casing and magnetizable by the actuator current to attract and thereby actuate the switching member to open the switch when the actuator current exceeds a predetermined level.

5. A circuit breaker according to claim 3 wherein the elongated expansion plunger comprises a plurality of longitudinally spaced transversely extending eddy current heating sections and intermediate thermally sensitive expansion plug sections longitudinally expandable by being heated whereby an AC casing current generates eddy currents in the eddy current heating sections to heat and thereby longitudinally expand the plug sectrons.

6. A circuit breaker according to claim 3 wherein the electrical conductor casing is a circumferentially split electrical conductor casing.

7. A circuit breaker according to claim 6 wherein the internal electrical circuit comprises connections to the split conductor casing at the circumferential ends of the split casing.

8. A circuit breaker according to claim 3 wherein the current responsive actuator comprises a plurality of electrical connectors longitudinally spaced along the conductor casing for connecting a selected length of the conductor casing in the internal circuit for thereby selecting the effective electrical impedance of the actuator.

9. A circuit breaker according to claim 3 wherein the elongated electrical conductor casing is a resistance casing providing resistance impedance for heating the expansion plunger.

10. A circuit breaker according to claim 9 wherein the elongated expansion plunger comprises a thermally sensitive elongated plastic expansion plug with embedded metal particles.

11. A circuit breaker according to claim 1 further comprising adjustment means for longitudinally adjusting the thrust support for adjusting said predetermined current level at which the switching member is actuated by the plunger to open the switch.

12. A current responsive actuator for actuating an associated device in accordance with the actuator current comprising an elongated tubular electrical conductor casing, a thrust support at the rear end of the casing, a thermally responsive expansion plunger mounted within the casing in engagement with the thrust support and longitudinally expandable upon being heated to actuate an associated device. the casing having spaced electrical connectors means and the actuator having an electrical impedance between the electrical connectors to electrically heat and thereby longitudinally expand the expansion plunger to actuate an associated device.

13. A current responsive actuator according to claim 12 wherein the electrical connector means comprises a first electrical connector and a plurality of longitudinally spaced second electrical connectors selectively useful with the first electrical connector for selecting the electrical impedance of the actuator.

14. A current responsive actuator for actuating an associated device in accordance with the actuator current comprising an elongated circumferentially tubular electrical resistance conductor casing. a rear thrust member longitudinally adjustable within a rear end of the casing, and a thermally sensitive expansion plunger mounted within the casing in engagement with the rear thrust member and longitudinally expandable upon being heated to actuate an associated device. a first electrical connector extending from one circumferential end of the split tubular casing and a plurality of Iongitudinally spaced second electrical connectors extending from the other circumferential end of the split tubular casing whereby an electrical current between the first connector and a selected second connector is operable to heat the electrical resistance casing and thereby heat the expansion plunger to longitudinally expand the expansion plunger and actuate an associ- 

1. In a circuit breaker having a pair of terminals, an internal electrical circuit breaker between the circuit breaker terminals comprising an electrical switch and a current responsive actuator, a switch operating device operable for opening and closing the switch and having a switching member actuated by the current responsive actuator when the actuator current exceeds a predetermined level to open the circuit breaker switch, the improvement wherein the current responsive actuator comprises a thrust support and an elongated thermally sensitive expansion plunger extending longitudinally from the thrust support and longitudinally expandable from the thrust support upon being heated to actuate the switching member to open the switch, the current responsive actuator having an electrical impedance in the internal electrical circuit effective to heat and thereby longitudinally expand the expansion plunger to actuate the switching member to open the switch when the actuator current exceeds said predetermined level.
 2. A circuit breaker according to claim 1 wherein the switch operating device comprises spring means for opening the switch and wherein the switching member is operative to latch the switch closed and is actuated by the longitudinal expansion of the expansion plunger to unlatch the switch to be opened with the spring means when the actuator current exceeds said predetermined level.
 3. A circuit breaker according to claim 1 wherein the current responsive actuator comprises an elongated electrical conductor casing for the elongated expansion plunger electrically connected in the internal electrical circuit.
 4. A circuit breaker according to claim 3 wherein the current responsive actuator comprises a generally U-shaped magnetizable magnet member partly surrounding the elongated electrical conductor casing and magnetizable by the actuator current to attract and thereby actuate the switching member to open the switch when the actuator current exceeds a predetermined level.
 5. A circuit breaker according to claim 3 wherein the elongated expansion plunger comprises a plurality of longitudinally spaced transversely extending eddy current heating sections and intermediate thermally sensitive expansion plug sections longitudinally expandable by being heated whereby an AC casing current generates eddy currents in the eddy current heating sections to heat and thereby longitudinally expand the plug sections.
 6. A circuit breaker according to claim 3 wherein the electrical conductor casing is a circumferentially split electrical conductor casing.
 7. A circuit breaker according to claim 6 wherein the internal electrical circuit comprises connections to the split conductor casing at the circumferential ends of the split casing.
 8. A circuit breaker according to claim 3 wherein the current responsive actuator comprises a plurality of electrical connectors longitudinally spaced along the conductor casing for connecting a selected length of the conductor casing in the internal circuit for thereby selecting the efFective electrical impedance of the actuator.
 9. A circuit breaker according to claim 3 wherein the elongated electrical conductor casing is a resistance casing providing resistance impedance for heating the expansion plunger.
 10. A circuit breaker according to claim 9 wherein the elongated expansion plunger comprises a thermally sensitive elongated plastic expansion plug with embedded metal particles.
 11. A circuit breaker according to claim 1 further comprising adjustment means for longitudinally adjusting the thrust support for adjusting said predetermined current level at which the switching member is actuated by the plunger to open the switch.
 12. A current responsive actuator for actuating an associated device in accordance with the actuator current comprising an elongated tubular electrical conductor casing, a thrust support at the rear end of the casing, a thermally responsive expansion plunger mounted within the casing in engagement with the thrust support and longitudinally expandable upon being heated to actuate an associated device, the casing having spaced electrical connectors means and the actuator having an electrical impedance between the electrical connectors to electrically heat and thereby longitudinally expand the expansion plunger to actuate an associated device.
 13. A current responsive actuator according to claim 12 wherein the electrical connector means comprises a first electrical connector and a plurality of longitudinally spaced second electrical connectors selectively useful with the first electrical connector for selecting the electrical impedance of the actuator.
 14. A current responsive actuator for actuating an associated device in accordance with the actuator current comprising an elongated circumferentially tubular electrical resistance conductor casing, a rear thrust member longitudinally adjustable within a rear end of the casing, and a thermally sensitive expansion plunger mounted within the casing in engagement with the rear thrust member and longitudinally expandable upon being heated to actuate an associated device, a first electrical connector extending from one circumferential end of the split tubular casing and a plurality of longitudinally spaced second electrical connectors extending from the other circumferential end of the split tubular casing whereby an electrical current between the first connector and a selected second connector is operable to heat the electrical resistance casing and thereby heat the expansion plunger to longitudinally expand the expansion plunger and actuate an associated device. 